Investigation of a Novel Light-blue-emitting Fluorescent Guest/Host System with Excellent Lifetime
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0916-DD01-05
Investigation of a Novel Light-blue-emitting Fluorescent Guest/Host System with Excellent Lifetime Philipp van Gemmern1, Stefan P. Grabowski2, Herbert Boerner2, Volker van Elsbergen2, HansPeter Löbl2, Edward Young2, Holger Heil3, Rocco Fortte3, Heinrich Becker3, Michael Heuken1,4, Holger Kalisch1, and Rolf H. Jansen1 1 Institut für Theoretische Elektrotechnik, RWTH Aachen, Kopernikusstrasse 16, Aachen, NRW, 52074, Germany 2 Philips Research Laboratories, Weisshausstrasse 2, Aachen, NRW, 52066, Germany 3 Merck OLED Materials GmbH, Industrial Park Höchst, Building F 821, Frankfurt/Main, HE, 65926, Germany 4 AIXTRON AG, Kackertstrasse 15-17, Aachen, NRW, 52072, Germany
ABSTRACT In this work, organic light emitting devices (OLEDs) based on a blue-emitting fluorescent guest/host system from Merck OLED Materials GmbH is investigated. OLEDs comprising a hole transport layer (HTL), the emissive film Merck Blue Host:Merck Blue Guest (MBH:MBG), a hole-blocking film and the electron transport layer (ETL) were prepared by vacuum thermal evaporation. The hole-blocking capabilities of aluminum(III)bis(2-methyl-8quinolinato)4-phenylphenolate (BAlq) and the host material MBH were investigated. By employing an additional hole-blocking layer, the current efficiency could be increased from 5.7 to 7.4 cd/A. Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyano-quinodimethane (F4-TCNQ) doping of the HTL was investigated. Devices with 4,7-diphenyl-1,10-phenanthroline (BPhen) or 1,3,5-Tris-(N-phenylbenzimidazol-2-yl)benzene (TPBI) as alternative ETLs were fabricated and conclusions were drawn regarding the charge balance in the devices. It was found that employing tris-(8-hydroxyquinoline) aluminum (Alq3) as ETL leads to the best lifetimes of about 2000 hours at a constant current of 20 mA/cm2 while p-doping in combination with BPhen as ETL leads to the highest efficiency of 5.7 lm/W max. and 4.4 lm/W at 1000 cd/m2. INTRODUCTION White organic light-emitting diodes (OLEDs) are promising candidates to substitute conventional light sources. Being extremely thin and diffusive light sources which can potentially be deposited even on flexible substrates, OLEDs offer a high grade of flexibility in terms of design and employment. With the theoretic potential to even exceed the efficiency and lifetime of fluorescent tubes, white OLEDs are of keen interest for lighting companies. A recent study of the Optoelectronics Industry Development Association (OIDA) showed that about 20% of all electricity produced in the United States is consumed for lighting purposes, costing 50 billion US dollars [1]. Considering these numbers, economic as well as ecologic advantages need no further explanation. Excellent color rendering is a key issue for lighting applications, which can only be achieved by mixing red, green and blue emission. While highly efficient and stable
phosphorescent organic emitters are available for the generation of green and red light, phosphorescent materials for blue emission with acceptable lifetimes and efficiencies are a t
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